U.S. patent application number 10/077944 was filed with the patent office on 2002-10-03 for piston control mechanism of reciprocating internal combustion engine of variable compression ratio type.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Aoyama, Shunichi, Hiyoshi, Ryosuke, Moteki, Katsuya, Ushijima, Kenshi.
Application Number | 20020139324 10/077944 |
Document ID | / |
Family ID | 18946310 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020139324 |
Kind Code |
A1 |
Moteki, Katsuya ; et
al. |
October 3, 2002 |
Piston control mechanism of reciprocating internal combustion
engine of variable compression ratio type
Abstract
In an internal combustion engine of variable compression ratio
type, a piston control mechanism is employed which comprises a
lower link rotatably disposed on a crank pin of a crankshaft of the
engine, an upper link having one end pivotally connected to the
lower link and the other end pivotally connected to a piston of the
engine, a control link having one end pivotally connected to the
lower link; and a position changing mechanism which changes a
supporting axis about which the other end of the control link
turns. When the piston comes up to a top dead center, a compression
load is applied to the control link in an axial direction of the
control link in accordance with an upward inertial load of the
piston.
Inventors: |
Moteki, Katsuya; (Tokyo,
JP) ; Aoyama, Shunichi; (Kawagawa, JP) ;
Ushijima, Kenshi; (Kanagawa, JP) ; Hiyoshi,
Ryosuke; (Kanagawa, JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
18946310 |
Appl. No.: |
10/077944 |
Filed: |
February 20, 2002 |
Current U.S.
Class: |
123/48B |
Current CPC
Class: |
F02B 75/048 20130101;
F02B 75/045 20130101 |
Class at
Publication: |
123/48.00B |
International
Class: |
F02B 075/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2001 |
JP |
2001-091742 |
Claims
What is claimed is:
1. A piston control mechanism of an internal combustion engine,
said engine including a piston slidably disposed in a piston
cylinder and a crankshaft converting a reciprocation movement of
said piston to a rotation movement, said piston control mechanism
comprising: a lower link rotatably disposed on a crank pin of said
crankshaft; an upper link having one end pivotally connected to
said lower link and the other end pivotally connected to said
piston; a control link having one end pivotally connected to said
lower link; and a position changing mechanism which changes a
supporting axis about which the other end of said control link
turns, wherein when said piston comes up to a top dead center, a
compression load is applied to said control link in an axial
direction of the control link in accordance with an upward inertial
load of said piston.
2. A piston control mechanism as claimed in claim 1, in which said
compression load is applied in a direction from a pivot axis
between said lower link and said control link to said supporting
axis.
3. A piston control mechanism as claimed in claim 2, in which when
said piston comes up to the top dead center, a rotation direction
of an upper link center line relative to a first direction line is
equal to a rotation direction of a control link center line
relative to a second direction line, said upper link center line
being an imaginary line which perpendicularly crosses both a first
pivot axis between said piston and said upper link and a second
pivot axis between said upper link and said lower link, said
control link center line being an imaginary line which
perpendicularly crosses both a third pivot axis between said lower
link and said control link and said supporting axis, said first
direction line being an imaginary line which perpendicularly
crosses both said second pivot axis and a center axis of said crank
pin, and said second direction line being an imaginary line which
perpendicularly crosses both said third pivot axis and said center
axis of said crank pin.
4. A piston control mechanism as claimed in claim 3, in which said
supporting axis is positioned more remote from said piston than
said third pivot axis.
5. A piston control mechanism as claimed in claim 1, in which said
position changing mechanism comprises: a control crankshaft which
extends in parallel with said crankshaft and rotates about a given
axis, said control crankshaft including a main shaft portion which
is rotatable about said given axis and an eccentric pin which is
radially raised from said main shaft portion, said eccentric pin
being received in a cylindrical bearing bore formed in the other
end of said control link; and an electric actuator which rotates
said control crankshaft about said given axis with the electric
power.
6. A piston control mechanism as claimed in claim 5, in which said
electric actuator is energized to rotate said control crankshaft
when changing of engine compression ratio is needed.
7. A piston control mechanism as claimed in claim 6, in which an
eccentric angle defined between a third direction line and said
control link center line at the top dead center of the position in
a higher compression condition of the engine is smaller than a
corresponding eccentric angle defined and established in a lower
compression ratio condition, said third direction line being an
imaginary line which perpendicularly extends across both the given
axis of said main shaft portion and a center axis of said eccentric
pin.
8. A piston control mechanism as claimed in claim 7, in which when,
under the higher compression condition of the engine, said piston
comes up to the top dead center, said eccentric angle is set
substantially 0 (zero) degree.
9. A piston control mechanism as claimed in claim 4, in which when
said piston is at the top dead center, said second pivot axis and
said third pivot axis are positioned at opposite sides with respect
to an imaginary plane which includes a center axis of a crank pin
of said crankshaft and is parallel with an axis of a piston
cylinder of the engine.
10. A piston control mechanism as claimed in claim 3, in which said
supporting axis is positioned closer to piston than said third
pivot axis.
11. A piston control mechanism as claimed in claim 10, in which
when said piston is at the top dead center, said second pivot axis
and said third pivot axis are positioned at the same side with
respect to an imaginary plane which includes a center axis of a
crank pin of said crankshaft and is parallel with an axis of a
piston cylinder of the engine.
12. A piston control mechanism of an internal combustion engine,
said engine including a piston slidably disposed in a piston
cylinder and a crankshaft converting a reciprocation movement of
said piston to a rotation movement, said piston control mechanism
comprising: a lower link rotatably disposed on a crank pin of said
crankshaft; an upper link having one end pivotally connected to
said lower link and the other end pivotally connected to said
piston; a control link having one end pivotally connected to said
lower link; and a position changing mechanism including a control
crankshaft which extends in parallel with said crankshaft and
rotates about a given axis, said control crankshaft including a
main shaft portion which is rotatable about said given axis and an
eccentric pin which is radially raised from said main shaft
portion, said eccentric pin being received in a cylindrical bearing
bore formed in the other end of said control link, wherein when
said piston comes up to a top dead center, a rotation direction of
an upper link center line relative to a first direction line is
equal to a rotation direction of a control link center line
relative to a second direction line, said upper link center line
being an imaginary line which perpendicularly crosses both a first
pivot axis between said piston and said upper link and a second
pivot axis between said upper link and said lower link, said
control link center line being an imaginary line which
perpendicularly crosses both a third pivot axis between said lower
link and said control link and said supporting axis, said first
direction line being an imaginary line which perpendicularly
crosses both said second pivot axis and a center axis of said crank
pin, and said second direction line being an imaginary line which
perpendicularly crosses both said third pivot axis and said center
axis of said crank pin.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates in general to reciprocating
internal combustion engines of a variable compression ratio type
that is capable of varying a compression ratio under operation
thereof and more particularly to the reciprocating internal
combustion engines of a multi-link type wherein each piston is
connected to a crankshaft through a plurality of links. More
specifically, the present invention is concerned with a piston
control mechanism of such internal combustion engines.
[0003] 2. Description of Related Art
[0004] In the field of reciprocating internal combustion engines,
there has been proposed a variable compression ratio type that is
capable of varying a compression ratio of the engine in accordance
with operation condition of the same. One of such engines is shown
in Laid-Open Japanese Patent Application (Tokkai) 2000-73804. The
engine of the publication employs a piston control mechanism
wherein each piston is connected to a crankshaft through a
plurality of links.
[0005] For ease of understanding of the present invention, the
piston control mechanism of the publication will be briefly
described with reference to FIG. 12 of the accompanying
drawings.
[0006] In the drawing, denoted by numeral 101 is a crankshaft
having crank pins 102. To each crank pin 102, there is pivotally
connected a lower link (floating lever) 103 at a middle portion
thereof. To one end of lower link 103, there is pivotally connected
a lower end of an upper link 106 through a first connecting pin
110. An upper end of the upper link 106 is pivotally connected to a
piston 104 through a piston pin 105. To the other end of lower link
103, there is pivotally connected a lower end of a control link 107
through a second connecting pin 111. An upper end of control link
107 is pivotally connected to an eccentric pin 109 of a control
crankshaft 108. More specifically, the lower and upper ends of
control link 107 are formed with respective cylindrical bearing
bores which pivotally receive second connecting pin 111 and
eccentric pin 109 respectively. Under operation of the engine,
control crankshaft 108 is turned in accordance with operation
condition of the engine, causing control link 107 to vary and set
pivoting movement of lower link 103 thereby varying or setting a
stroke of the piston 104. With this operation, the compression
ratio of the engine is varied in accordance with the engine
operation condition.
SUMMARY OF INVENTION
[0007] In the piston control mechanism as mentioned hereinabove,
based on both an upward inertial load applied to piston 104 when
piston 104 moves upward and a downward load applied to the same
when combustion takes place, a certain load is inevitably applied
to control link 107 through upper link 106 and lower link 103. In
control links like the control link 107 of which both ends are
formed with cylindrical bearing bores, it is known that an elastic
deformation appearing on control link 107 when a tensile load is
applied thereto is greater than that appearing when a compression
load is applied thereto. That is, variation of effective length of
control link 107 in case of receiving the tensile load is larger
than that in case of receiving the compression load. That is, in
case of the compression load, only a shaft portion proper of
control link 107 defined between the two cylindrical bearing bores
is subjected to an elastic deformation, while, in case of tensile
load, the entire length of control link 107 including the two
thinner cylindrical bearing bores is subjected to the elastic
deformation inducing the increase in elastic deformation
degree.
[0008] When piston 104 comes up to a top dead center (TDC) on
exhaust stroke, upward inertial load of piston 104 brings the crown
of the same into a position closest to intake and exhaust valves.
Furthermore, when, due to valve overlapping or the like, intake and
exhaust valves are still open partially at such top dead center
(TDC), the piston crown becomes much closer to the intake and
exhaust valves. Thus, when, with piston 104 taking the top dead
center (TDC) on exhaust stroke, a certain tensile load is applied
to control link 107 based on the upward inertial load of piston
104, the elastic deformation of control link 107 becomes remarkable
causing piston 104 to be displaced from a proper position, which
tends to deteriorate engine performance. Furthermore, if the
displacement of piston 104 becomes remarkably large, undesirable
interference between piston 104 and intake and exhaust valves may
occur.
[0009] Accordingly, an object of the present invention is to
provide a piston control mechanism of reciprocating internal
combustion engine, which is free of the above-mentioned undesired
piston displacement.
[0010] Another object of the present invention is to provide a
piston control mechanism of reciprocating internal combustion
engine of variable compression ratio type, which can assuredly
avoid interference between a piston and intake and exhaust valves
without sacrificing engine performance, that is, without narrowing
a range in which the engine compression ratio is variable.
[0011] Still another object of the present invention is to provide
a piston control mechanism of reciprocating internal combustion
engine of variable compression ratio type, which is compact in size
and exhibits a high cost performance.
[0012] According to a first aspect of the present invention, there
is provided a piston control mechanism of an internal combustion
engine, the engine including a piston slidably disposed in a piston
cylinder and a crankshaft converting a reciprocation movement of
the piston to a rotation movement, the piston control mechanism
comprising a lower link rotatably disposed on a crank pin of the
crankshaft; an upper link having one end pivotally connected to the
lower link and the other end pivotally connected to the piston; a
control link having one end pivotally connected to the lower link;
and a position changing mechanism which changes a supporting axis
about which the other end of the control link turns, wherein when
the piston comes up to a top dead center, a compression load is
applied to the control link in an axial direction of the control
link in accordance with an upward inertial load of the piston.
[0013] According to a second aspect of the present invention, there
is provided a piston control mechanism of an internal combustion
engine, the engine including a piston slidably disposed in a piston
cylinder and a crankshaft converting a reciprocation movement of
the piston to a rotation movement, the piston control mechanism
comprising a lower link rotatably disposed on a crank pin of the
crankshaft; an upper link having one end pivotally connected to the
lower link and the other end pivotally connected to the piston; a
control link having one end pivotally connected to the lower link;
and a position changing mechanism including a control crankshaft
which extends in parallel with the crankshaft and rotates about a
given axis, the control crankshaft including a main shaft portion
which is rotatable about the given axis and an eccentric pin which
is radially raised from the main shaft portion, the eccentric pin
being received in a cylindrical bearing bore formed in the other
end of the control link, wherein when the piston comes up to a top
dead center, a rotation direction of an upper link center line
relative to a first direction line is equal to a rotation direction
of a control link center line relative to a second direction line,
the upper link center line being an imaginary line which
perpendicularly crosses both a first pivot axis between the piston
and the upper link and a second pivot axis between the upper link
and the lower link, the control link center line being an imaginary
line which perpendicularly crosses both a third pivot axis between
the lower link and the control link and the supporting axis, the
first direction line being an imaginary line which perpendicularly
crosses both the second pivot axis and a center axis of the crank
pin, and the second direction line being an imaginary line which
perpendicularly crosses both the third pivot axis and the center
axis of the crank pin.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a sectional view of an internal combustion engine
having a piston control mechanism of a first embodiment, showing a
piston assuming a top dead center (TDC) under a higher compression
ratio condition;
[0015] FIG. 2 is a view similar to FIG. 1, but showing the piston
assuming the top dead center (TDC) under a lower compression ratio
condition;
[0016] FIGS. 3A, 3B and 3C are illustrations of a control link,
showing variation of elastic deformation depending on loading
direction;
[0017] FIG. 4 is a graph showing a relation between a load applied
to a control link and an elastic deformation appearing on the
control link;
[0018] FIG. 5 is a graph showing a relation between a load inputted
to a control crankshaft and a bending deformation appearing on the
control crankshaft;
[0019] FIGS. 6A and 6B are front and sectional views of a unit
including the control crankshaft and the control link, showing the
bending deformation of the control crankshaft appearing when a load
is applied thereto in a first direction;
[0020] FIGS. 7A and 7B are views similar to FIGS. 6A and 6B, but
showing the bending deformation of the control crankshaft appearing
when a load is applied thereto in a second direction;
[0021] FIGS. 8A and 8B are views similar to FIGS. 6A and 6B, but
showing the bending deformation of the control crankshaft appearing
when a load is applied thereto in a third direction;
[0022] FIGS. 9A and 9B are partial front views of the unit
including the control crankshaft and the control link, showing
difference of bending deformation of control crankshaft depending
on a direction in which a load is applied;
[0023] FIG. 10 is a view similar to FIG. 1, but showing a second
embodiment of the present invention;
[0024] FIG. 11 is a view similar to FIG. 1, but showing a third
embodiment of the present invention; and
[0025] FIG. 12 is a sectional view of an internal combustion engine
of known variable compression ratio type.
DETAILED DESCRIPTION OF EMBODIMENTS
[0026] In the following, various embodiments of the present
invention will be described in detail with reference to the
accompanying drawings.
[0027] For ease of understanding, various directional terms, such
as, right, left, upper, lower, rightward, etc., are contained in
the description. However, such terms are to be understood with
respect to only drawing or drawings on which corresponding part or
portion is illustrated.
[0028] Furthermore, for simplification of description, throughout
the description, substantially same parts and constructions are
denoted by the same numerals and repeated explanation of them will
be omitted.
[0029] Referring to FIGS. 1 to 9A and 9B, particularly FIGS. 1 and
2, there is shown a piston control mechanism of a first embodiment
of the present invention, which is applied to a reciprocating
internal combustion engine of variable compression ratio type.
[0030] As is seen from FIG. 1, the piston control mechanism 100A of
the first embodiment comprises a lower link 11 which is rotatably
disposed on a crank pin 2 of a crankshaft 1 of an associated
internal combustion engine at a center opening thereof. A center
axis of crank pin 2 is denoted by reference P6. The lower link 11
is shaped generally triangle. An upper link 13 is pivotally
connected at a lower end to lower link 11 through a first
connecting pin 12 and pivotally connected at an upper end to a
piston 3 through a piston pin 4. A center axis of first connecting
pin 12 is denoted by reference P2 and a center axis of piston pin 4
is denoted by reference P1. A control link 15 is pivotally
connected at an upper end to lower link 11 through a second
connecting pin 14 and pivotally connected at a lower end to a body
of the engine trough a position changing mechanism 16. A center
axis of second connecting pin 14 is denoted by reference P3. As
will be described in detail hereinafter, position changing
mechanism 16 is constructed to change a supporting axis P4 about
which the lower end of control link 15 turns. Thus, the degree of
freedom of lower link 11 is controlled.
[0031] As shown, piston 3 is slidably received in a cylinder 6
defined in a cylinder block 5. A piston head 3a of piston 3 is
formed with a recess that constitutes part of a combustion
chamber.
[0032] The position changing mechanism 16 comprises a control
crankshaft 17 which substantially extends in parallel with
crankshaft 1 and an electric actuator which rotates control
crankshaft 17 about its center axis P5 in accordance with an
operation condition of the engine.
[0033] As is seen from FIGS. 6A and 6B, control crankshaft 17
comprises a main shaft portion 18 which rotates about the center
axis P5, paired crank arms 20 which extend radially outward from
the main shaft portion 18 and an eccentric pin 19 which is held
between the paired crank arms 20 at a position eccentric to main
shaft portion 18. Eccentric pin 19 is of a cylindrical solid member
of which center axis P4 is the supporting axis P4 of control link
15. The cylindrical eccentric pin 19 is received in a cylindrical
bearing bore 23 formed in a lower end of control link 15. (It is to
be noted that FIGS. 6A and 6B (and FIGS. 7A to 8B) are
exaggeratedly illustrated.) Control link 15 is formed at an upper
end with a cylindrical bearing bore 21 which rotatably receives
second connecting pin 14.
[0034] As is seen from FIG. 6B, the center axis P4 of the eccentric
pin 19 (viz., supporting axis P4 of control link 15) is eccentric
to the center axis P5 of main shaft portion 18 of control
crankshaft 17.
[0035] For achieving easy mounting onto crank pin 2 and eccentric
pin 19, lower link 11 and control link 15 are constructed to have a
split structure.
[0036] When, in operation, control crankshaft 17 (see FIG. 1) is
turned by the electric actuator about its center axis P5 in
accordance with the engine operation condition, the lower end of
control link 15 is subjected to position change and thus behavior
of lower link 11 changes thereby to change the stroke of piston 3,
resulting in that the compression ratio of the engine is
varied.
[0037] FIGS. 3A, 3B and 3C schematically show variation of elastic
deformation of control link 15 that appears when a load is applied
thereto in different directions. These drawings respectively show a
compressed condition wherein control link 15 is applied with a
compression load, a neutral condition wherein control link 15 has
no load applied thereto and an extended condition wherein control
link 15 is applied with a tensile load. For ease of understanding,
control link 15 and deformation of the same are illustrated
exaggeratingly.
[0038] As is seen from these drawings, control link 15 is formed at
an upper boss portion (viz., first boss portion) 22 with the
cylindrical bearing bore 21 through which second connecting pin 14
passes, and at a lower boss portion (viz., second boss portion) 24
with the cylindrical bearing bore 23 through which eccentric pin 19
passes.
[0039] If the distance between respective axes of pins 14 and 19
that pass through bores 21 and 23 of control link 15 is assumed as
an effective length of control link 15, the effective length has
the following tendency that depends on a direction in which a load
is applied to control link 15.
[0040] That is, as is seen from the drawings, a difference between
effective length D3 of link 15 in the extended condition and
effective length D1 of link 15 in neutral condition is greater than
that between effective length D2 of link 15 in the compressed
condition and effective length D1 of link in neutral condition.
[0041] The reasons of this phenomenon may be as follows.
[0042] That is, in case of applying a compression load to control
link 15 (viz., FIG. 3A), only a main shaft portion 25 of link 15 is
compressed leaving upper and lower boss portions 22 and 24 not
compressed. While, in case of applying a tensile load to control
link 15 (viz., FIG. 3C), not only main shaft portion 25 but also
upper and lower boss portions 22 and 24 of link 15 are extended
axially outward, and thus, the above-mentioned phenomenon takes
place.
[0043] As is known, when, under operation of the engine, piston 3
comes up to a top dead center (TDC) particularly on exhaust stroke,
a remarked upward inertia load F1 (see FIG. 1) is applied to piston
3. This inertia load tends to bring piston 3 to a position closest
to the intake and exhaust valves. Accordingly, when, due to valve
overlapping or the like, the intake and exhaust valve are still
open partially at such top dead center (TDC), piston 3 becomes much
closer to the intake and exhaust valves increasing a possibility of
undesirable contact of piston crown with the intake and exhaust
valves.
[0044] In order to assuredly avoid such undesired contact, the
following measures are practically employed in the first embodiment
100A of the present invention.
[0045] That is, as is seen from FIG. 1, at the time when piston 3
comes up to the top dead center (TDC), a downward load F2 applied
to control link 15 caused by an upward inertial load F1 of piston 3
through upper link 13 and lower link 11 is adjusted to operate in a
direction coincident with an imaginary line that extends through
both center axis P3 of second connecting pin 14 and supporting axis
P4 of control link 15 (viz., center axis P4 of eccentric pin 19.
That is, piston control mechanism 100A of the first embodiment is
so arranged that upon piston 3 reaching the top dead center (TDC),
control link 15 is just applied with the compression load.
[0046] The measures of the first embodiment 100A will be much
clearly understood from the following description.
[0047] Let us call an imaginary line perpendicularly crossing both
center axis P1 of piston pin 4 and center axis P2 of first
connecting pin 12 as an upper link center line 13A, an imaginary
line perpendicularly crossing both center axis P3 of second
connecting pin 14 and supporting axis P4 of control link 15 (viz.,
center axis P4 of eccentric pin 19) as a control link center line
15A, an imaginary line perpendicularly crossing both center axis P2
of first connecting pin 12 and center axis P6 of crank pin 2 as a
first direction line H1 and an imaginary line perpendicularly
crossing both center axis P3 of second connecting pin 14 and center
axis P6 of crank pin 2 as a second direction line H2. As shown, in
the first embodiment 100A, when piston 3 is at the top dead center
(TDC), a rotation direction al of upper link center line 13A
relative to first direction line H1 is equal to a rotation
direction .alpha.2 of control link center line 15A relative to
second direction line H2.
[0048] When an upward load F3 is applied to lower link 11 along
upper link center line 13A from upper link 13 based on upward
inertial load F1, lower link 11 is applied with a torque about
center axis P6 of crank pin 2 in the same direction as direction
.alpha.1. Since direction .alpha.2 is set equal to direction
.alpha.1, a load applied to control link 15 according to the torque
functions to compress control link 15, that is, to apply control
link 15 with a compression load. It is to be noted that if the
rotation direction of control link center line 15A relative to
second direction line H2 is opposite to the above-mentioned
direction .alpha.1, the load would function to extend control link
15, that is, to apply control link 15 with a tensile load, which is
not preferable.
[0049] As is understood from the above description, in the first
embodiment 100A, when piston 3 comes up to the top dead center
(TDC), control link 15 is applied with a compression load and thus,
the elastic deformation of control link 15 is considerably reduced.
This is very advantageous when piston comes up to the top dead
center (TDC) on exhaust stroke. Accordingly, the above-mentioned
undesirable upward displacement of piston 3 at the top dead center
on exhaust stroke is suppressed, and thus, the possibility of
undesirable contact of piston crown 3a with the intake and exhaust
valves is suppressed. With this advantageous operation, there is no
need of narrowing a range in which the engine compression ratio is
varied, and thus, engine performance can be improved.
[0050] When now piston 3 is at the top dead center (TDC) on
compression stroke wherein a downward load is applied to piston 3
due to the fuel combustion in combustion chamber, the load applied
to the control link 15 functions to extend the same, that is, to
apply the same with a tensile load. Thus, the elastic deformation
of control link 15 becomes relatively large. However, since, in the
compression stroke, both the intake and exhaust valves are kept
closed and the load applied to piston 3 is directed downward, there
is no possibility of contact of piston crown 3a with the intake and
exhaust valves. Furthermore, lowering of thermal efficiency of the
engine caused by such elastic deformation of control link 15 at the
top dead center (TDC) on compression stroke is relatively small.
That is, the deformation of control link 15 is not just a
deformation but an elastic deformation that has an elastic energy
as a potential energy. It is thought that, under operation of
engine, part of energy produced as a result of fuel combustion in
combustion chamber is stored in the engine body as the elastic
energy, and when piston 3 comes down while reducing the load, the
stored energy is used for assisting rotation of crankshaft 1.
[0051] In the following, elastic deformation of control crankshaft
17 will be described with reference to FIGS. 5 to 9B. It is to be
noted that parts shown in these drawings are illustrated
exaggeratingly for ease of understanding.
[0052] As is seen from FIG. 6A, in control crankshaft 17, center
axis P4 of eccentric pin 19 to which lower end of control link 15
is pivotally connected is eccentric to center axis P5 of main shaft
portion 18 of control crankshaft 17. Thus, under operation of
engine, a certain bending moment is applied to control crankshaft
17 from control link 15. A bending deformation of control
crankshaft 17 caused by such bending moment varies in accordance
with a direction in which the load is applied to eccentric pin
19.
[0053] That is, as is seen from FIGS. 6A and 6B, in case wherein
the load is directed from center axis P5 of main shaft portion 18
of control crankshaft 17 to center axis P4 of eccentric pin 19 of
control crankshaft 17, the bending deformation of control
crankshaft 17 exhibits the smallest value as is indicated by the
characteristic line L-1 of graph of FIG. 5. While, as is seen from
FIGS. 7A and 7B, in case wherein the load is directed from center
axis P4 of eccentric pin 19 to center axis P5 of main shaft portion
18, the bending deformation of control crankshaft 17 exhibits the
greatest value as is indicated by the characteristic line L-2 of
FIG. 5. While, as is seen from FIGS. 8A and 8B, in case wherein the
load is directed perpendicular to a third direction line H3 which
perpendicularly extends across both center axis P5 of main shaft
portion 18 and center axis P4 of eccentric pin 19, the bending
deformation of control crankshaft 17 exhibits an intermediate value
as is indicated by the characteristic line L-3 of FIG. 5.
[0054] The reason of this phenomenon will be described in the
following with reference t FIGS. 9A and 9B.
[0055] In case wherein as shown in FIG. 9A the load is directed
from center axis P4 of eccentric pin 19 to center axis P5 of main
shaft portion 18, eccentric pin 19 is applied at axial edges 26 of
a radially inside part thereof with a tensile load and thus the
bending deformation of control crankshaft 17 is large. Actually,
control crankshaft 17 exhibits a lower rigidity at eccentric pin
19. While, in case wherein as shown in FIG. 9B the load is directed
from center axis P5 of main shaft portion 18 to center axis P4 of
eccentric pin 19, eccentric pin 19 is applied at axial edges 26 of
the radially inside part thereof with a compression load and thus
the bending deformation of control crankshaft 17 is small.
[0056] The bending deformation of control crankshaft 17 directly
causes the undesired displacement of piston 3 from a proper
position. Thus, when the bending deformation of control crankshaft
17 is large, piston 3 shows a marked displacement at the top dead
center (TDC) on exhaust stroke, which tends to increase the
possibility of inducting the undesired contact of piston crown 3a
with the intake and exhaust valves. Since, in a higher compression
ratio condition as shown in FIG. 1, the top dead center (TDC) of
piston 3 is positioned higher than that in a lower compression
ratio condition as shown in FIG. 2, such undesired possibility is
increased.
[0057] In view of this, in the piston control mechanism of the
first embodiment 100A, there is employed such a measure that in the
higher compression ratio condition the bending deformation of
control crankshaft 17 at the top dead center (TDC) of piston 3 is
made smaller than that in the lower compression ratio condition.
More specifically, the bending deformation of control crankshaft 17
at the top dead center of piston 3 is gradually reduced as the
compression ratio set is increased.
[0058] That is, as will be understood when comparing the drawings
of FIGS. 1 and 2, a so-called eccentric angle .theta.H defined
between third direction line H3 (see FIG. 8B) and control link
center line 15A at the top dead center of piston 3 in the higher
compression ratio condition (FIG. 1) is set smaller than an
eccentric angle .theta.L defined in the lower compression ratio
condition (FIG. 2).
[0059] Accordingly, when, under the higher compression ratio
condition, piston 3 comes up to the top dead center (TDC), the
bending deformation of control crankshaft 17 is sufficiently
restrained thereby suppressing or at least minimizing undesired
upward displacement of piston 3 from its proper position (viz.,
regulated top dead center). Thus, undesired contact of piston crown
3a with the intake and exhaust valves is assuredly prevented. This
means permission of enlargement of the range in which the engine
compression ratio can be varied.
[0060] Furthermore, as is seen from FIGS. 1 and 2, in the first
embodiment 100A, when piston 3 is at the top dead center, center
axis P2 of first connecting pin 12 and center axis P3 of second
connecting pin 14 are positioned at opposite sides with respect to
an imaginary plane B that includes center axis P6 of crank pin 2 of
crankshaft 1 and is parallel with an axis of a piston cylinder 6 of
the engine, and supporting axis P4 of control link 15 is positioned
below center axis P3 of second connecting pin 14.
[0061] Accordingly, control crankshaft 17 whose eccentric pin 19
passes through the lower end of control crankshaft 15 can be
located in an obliquely lower zone of crankshaft 1 in cylinder
block 5, which usually offers a larger space. Thus, control
crankshaft 17 and its associated parts can be compactly and readily
installed in cylinder block 5 without changing the shape of the
same.
[0062] Referring to FIG. 10, there is shown a piston control
mechanism 100B of a second embodiment of the present invention.
[0063] In this embodiment 100B, when piston 3 is at the top dead
center (TDC), center axis P2 of first connecting pin 12 and center
axis P3 of second connecting pin 14 are positioned at the same side
with respect to the imaginary plane B that includes center axis P6
of crank pin 2 of crankshaft 1 and is parallel with the axis of
cylinder 6 of the engine, and supporting axis P4 of control link 15
is positioned above center axis P3 of second connecting pin 14.
That is, control link 15 extends diagonally upward from lower link
11, which causes positioning of control crankshaft 17 above
crankshaft 1. Thus, as compared with the above-mentioned first
embodiment 100A, the second embodiment 100B is somewhat poor in
layout.
[0064] However, also in the second embodiment 100B, when piston 3
is at the top dead center (TDC), a rotation direction P1 of upper
link center line 13A relative to first direction line H1 is equal
to a rotation direction .beta.2 of control link center line 15A
relative to second direction line H2. Accordingly, when piston 3
comes up to dead top center on exhaust stroke, a load F2 applied to
control link 15 functions to compress the same and thus bending
deformation of control crankshaft 17 is minimized thereby
suppressing or at least minimizing undesired upward displacement of
piston 3 at the top dead center. Thus, possibility of undesirable
contact of piston crown 3a with the intake and exhaust valves is
suppressed.
[0065] Referring to FIG. 11, there is shown a piston control
mechanism 100C of a third embodiment of the present invention.
[0066] In this third embodiment 100C, when, under a higher
compression ratio condition, piston 3 comes up to the top dead
center on exhaust stroke, the eccentric angle .theta.H defined
between third direction line H3 (see FIG. 8B) and control link
center line 15A is set 0 (zero) degree. Accordingly, in this third
embodiment 100C, under the condition wherein piston crown 3a comes
to a position closes to the intake and exhaust valves, the bending
deformation of control crankshaft 17 is most effectively suppressed
and thus the possibility of contact of piston crown 3a with the
intake and exhaust valves is assuredly suppressed.
[0067] The entire contents of Japanese Patent Application
2001-091742 filed Mar. 28, 2001 are incorporated herein by
reference.
[0068] Although the invention has been described above with
reference to the embodiments of the invention, the invention is not
limited to such embodiments as described above. Various
modifications and variations of such embodiments may be carried out
by those skilled in the art, in light of the above description.
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